Neutral CGM as damped Ly ? absorbers at high redshift

Recent searches for the hosts of high-redshift ($z \sim 4$) damped Ly$\alpha$ absorbers (DLAs) have detected bright galaxies at distances tens kpc from DLA. Using FIRE-2 cosmological zoom simulations, we argue that these relatively large are due to a predominantly cool and neutral inner circumgalactic medium (CGM) surrounding galaxies. The CGM is because short cooling time hot gas in $\lesssim10^{12}$ Msun halos, which implies accretion feedback energy radiated quickly, while it high volume densities column redshift shield photoionization. Our analysis predicts DLA covering factors ($\gtrsim50\%$) out impact parameters $\sim0.3((1 + z)/5)^{3/2}\ R_{\rm vir}$ central $z > 1$, equivalent physical distance $\sim 21 M_{12}^{1/3} ((1 z)/5)^{1/2}$ ($R_{\rm $M_{12}$ halo virial radius mass units $10^{12}$ Msun, respectively). This 4$ may be comparable unity 10$ times larger than stellar half-mass radii. A early universe suggests its metallicity can directly constrained by absorption surveys, without resorting ionization corrections as required ionized CGM.